1. Technical Field
The present invention generally relates to Fischer-Tropsch conversion of carbon monoxide and hydrogen to hydrocarbons having two or more carbon atoms (C2+ hydrocarbons). More particularly, the present invention relates to a high shear process for improving Fischer-Tropsch conversion of synthesis gas (i.e., a mixture of carbon monoxide and hydrogen) into hydrocarbons.
2. Background of the Invention
The Fischer-Tropsch process is utilized for the conversion of carbonaceous feedstock, e.g., coal or natural gas, to higher value liquid fuel or petrochemicals. Large quantities of methane, the main component of natural gas, are available in many areas of the world. Methane may be reformed with water or partially oxidized with oxygen to produce carbon monoxide and hydrogen (i.e., syngas or synthesis gas). Coal and other solid materials may also be used as starting raw materials from which synthesis gas may be produced.
Preparation of Hydrocarbons from Synthesis Gas is Well Known in the Art and is Usually referred to as Fischer-Tropsch synthesis, the Fischer-Tropsch process, or Fischer-Tropsch reaction(s). Catalysts for use in such synthesis usually contain a catalytically active metal of Groups 8, 9, 10 (in the new notation for the periodic table of the elements). In particular, iron, cobalt, nickel, and ruthenium may be used as the catalytically active metal. Cobalt and ruthenium have been found to be especially suitable for catalyzing a process in which synthesis gas is converted to primarily hydrocarbons having five or more carbon atoms (i.e., where the C5+ selectivity of the catalyst is high). A Fischer-Tropsch catalyst may also be promoted with other metals.
Catalytic hydrogenation of carbon monoxide by Fischer-Tropsch may produce a variety of products ranging from methane to higher alkanes and aliphatic alcohols. Fischer-Tropsch synthesis reactions are very exothermic and reaction vessels must be designed for adequate heat exchange capacity. Because the reactants for Fischer-Tropsch are gases while the product streams include liquids and waxes, the system is typically designed to continuously produce and remove therefrom a desired range of liquid and wax hydrocarbon products.
Research continues on developing more efficient Fischer-Tropsch catalyst systems and reaction systems that increase the selectivity for higher-value hydrocarbons in the Fischer-Tropsch product stream. In particular, a number of studies describe the behavior of iron, cobalt or ruthenium based catalysts in various reactor types, together with the development of catalyst compositions and preparations.
There are significant differences in the molecular weight distributions of the hydrocarbon products from Fischer-Tropsch reaction systems. Product distribution and/or product selectivity depends on the type and structure of the catalysts and on the reactor type and operating conditions. In general, however, the Fischer-Tropsch process yields an abundance of higher molecular weight wax-like compounds. Lower temperature Fischer-Tropsch operation generally produces heavier hydrocarbon products. In conventional Fischer-Tropsch processes, the higher molecular weight materials are subsequently cracked to lower molecular weight liquids for use as fuels and chemical feedstocks. Therefore, it is desirable to maximize the selectivity of the Fischer-Tropsch synthesis to the production of high-value liquid hydrocarbons, for example hydrocarbons with five or more carbon atoms per hydrocarbon chain.
Accordingly, there is a need in industry for improving production of liquid and gaseous hydrocarbons via catalytic Fischer-Tropsch conversion of synthesis gas.